Hip, trendy. A 'swankified club' would be one that all the cool people go to, that is a lot of fun, and that is basically just a really happening place. Swankified is a word used by only a select number of people, who truly understand it's meaning. The word is generally associated with the Oz Dust Ballroom- in fact, word has it that it's the most swankified place in town.

Fiyero: So! What's the most swankified place in town?
Galinda: That would be the Oz Dust Ballroom!
Fiyero: Sounds perfect!